1. Field of the Invention
The present invention relates to an ejector system for a vehicle and an ejector system controller, and more particularly to an ejector system for a vehicle having an ejector supplying a negative pressure to brake booster and an ejector system controller.
2. Description of the Related Art
In a conventional vehicle, in order to supply a brake booster with negative pressure that is greater than the negative pressure that is to be applied from an intake passage of the intake system, which provides communication between the atmosphere and each cylinder of an internal combustion engine, an ejector was used. The following vehicle controller has been described with regard to this ejector, for example in Japanese Patent Application Publication No. JP-A-2005-69175. In the vehicle controller, because the amount of intake air changes when the ejector operates, it is not possible to maintain a proper air-fuel ratio when idling. In consideration of this unstable idling, operation of the ejector is prohibited for a prescribed period of time after the internal combustion engine is started in order to establish stable idling and the proper air-fuel ratio in particular immediately after the engine is started.
The following negative pressure generating apparatus is described, for example, in Japanese Patent Application Publication No. JP-A-2004-299567. The negative pressure generating apparatus allows all of the intake air to flow into the ejector when the throttle valve is fully open, and further has a valve body that changes the cross-sectional area of the ejector nozzle and diffuser to adjust the intake air amount by controlling the valve body. According to the negative pressure generating apparatus described in JP-A-2004-299567, it is possible to prevent unstable idling even if the ejector is actuated, the result of which is that it is possible to perform proper intake control and possible to obtain a high negative pressure.
In recent years, environmental issues such as global warming and atmospheric pollution have gained more and more attention, making it an important issue to reduce emissions such as hydrocarbons included in vehicular exhaust gas. Quickly raising the temperature of a catalyst installed in an exhaust system of an internal combustion engine to the catalyst reaction temperature is one effective approach. For this reason, the ignition timing of the internal combustion engine is generally retarded after the internal combustion engine is started until the catalyst is activated. Simultaneously, the throttle valve is controlled so that the intake passage is increased, thereby increasing the intake air amount, which compensates for a decrease in torque (the control is hereinafter referred to as “catalyst warm-up control”). By performing the catalyst warm-up control, because it is possible to combust more gas mixture closer to the timing of the exhaust stroke, the catalyst may be quickly brought to the reaction temperature.
However, if the throttle valve is used to increase the intake passage as described above, the negative pressure generated in the internal combustion engine is reduced. In this case, because the brake booster is applying negative pressure from the intake system of the internal combustion engine, the brake assist function becomes insufficient, resulting in an increase in the operating load placed on the vehicle operator. For this reason, under the catalyst warm-up control as described above, an ejector is generally used to supply a greater negative pressure to the brake booster, in which case because the intake passage is opened relatively widely, there is a relative decrease in the degree of variation in the air intake amount even if the ejector is caused to function. For this reason, in contrast to the problem envisioned in the art proposed in JP-A-2005-69175 and JP-A2004-299567, there is no great loss of idling stability.
On the other hand, when the coolant temperature of the internal combustion engine reaches or exceeds a prescribed temperature and the catalyst is activated, there is no need to perform catalyst warm-up control. In this case, in order to lower the target rpm idling speed for improving fuel economy, the opening of the throttle valve is appropriately reduced. However, if the ejector is caused to function in this case, the air-fuel ratio is affected. This makes it difficult to control the target idling rpm speed, which could result in unstable idling. Although the simplest solution for this is to not cause the ejector to function, this results in the following problems. Because the structure of an ejector is one in which a large negative pressure is generated by the venturi effect, the passage corresponding to the part of the ejector in which the large negative pressure is generated is narrowed. If the ejector is not operated for a long period of time, because the intake air does not pass through the ejector, the passage tends to become blocked. The blockage may be caused by, for example, moisture contained in the intake air is condensed and then accumulated in the passage, and it can freeze in winter, intake air containing oil intrudes into the ejector to become attached the wall surfaces of the passage, and further joins with dust at the wall surfaces. As a result, it becomes a deposit that gradually blocks the passage.
The blockage of the ejector can occur as long as there is a time when the ejector does not operate, for example even in the ejector to which the vehicle controller described in JP-A-2005-69175 is applied. However, JP-A-2005-69175 makes no particular mention with regard to this point. In contrast, in the negative pressure generating apparatus of JP-A-2004-299567, because idling may be controlled as the intake air is continuously allowed to flow through the ejector, it is possible to achieve stable idling while inhibiting the risk of blockage of the ejector due to such deposits as described above. The negative pressure generating apparatus of JP-A-2004-299567 has a characteristic structure. For this reason, in order to retrofit this negative pressure generating apparatus to a vehicle that has an ejector, it would be necessary not only to change the control, but also to replace the negative pressure generating apparatus and the already installed ejector, and change the control wiring and the controller, resulting in a great increase in cost.